1. Field of the Invention
The present invention relates to a single step process for the nucleation and subsequent epitaxial growth on a lattice mismatched substrate.
2. Description of Related Art
Heteroepitaxial growth of GaN and related alloys on severely mismatched substrates such as sapphire, SiC and silicon requires thin nucleation layers to provide nucleation sites to initiate crystal growth. When optimized, these nucleation layers accommodate the strain between the substrate and epitaxial layers caused by lattice and thermal mismatches, while still maintaining crystallographic registration of the epitaxial films to the substrate lattice structure. The most commonly accepted practice for nucleation of these substrates with GaN-based material utilizes a two-temperature process involving either one or two flow paths. In addition, different growth pressures are used on certain steps in the nucleation process. In this fashion, high structural and electrical quality epitaxial films can be realized in severely mismatched material systems.